RESUMEN
Cyclic loading induces fatigue in bone and initiates a complex, functionally adaptive response. We investigated the effect of a single period of fatigue on the histologic structure and biomechanical properties of bone. The ulnae of 40 rats were subjected to cyclic fatigue (-6000 microepsilon) unilaterally until 40% loss of stiffness developed, followed by 14 days of adaptation. The contralateral ulna served as a treatment control (n = 20 rats), and a baseline loaded/non-loaded group (n = 20 rats/group) was included. Bones from 10 rats/group were examined histologically and the remaining bones (10 rats/group) were tested mechanically. The following measurements were collected: volumetric bone mineral density (vBMD); ultimate force (Fu); stiffness (S); energy-to-failure (U); cortical area (Ct.Ar); microcrack density (Cr.Dn); microcrack mean length (Cr.Le); microcrack surface density (Cr.S.Dn); osteocyte density (Ot.N/T.Ar and Ot.N/TV); bone volume fraction (B.Ar/T.Ar); resorption space density (Rs.N/Ct.Ar); and maximum and minimum area moments of inertia (IMAX and IMIN). Using confocal microscopy, the bones were examined for diffuse matrix injury, canalicular disruption, and osteocyte disruption. The adapted bones had increased B.Ar, IMAX, and IMIN in the mid-diaphysis. Fatigue loading decreased structural properties and induced linear microcracking. At 14 days, adaptation restored structural properties and microcracking was partially repaired. There was a significant nonlinear relationship between Ot.N/T.Ar and B.Ar/T.Ar during adaptation. Disruption of osteocytes was observed adjacent to microcracks immediately after fatigue loading, and this did not change after the period of adaptation. In fatigue-loaded bone distant from microcracks, diffuse matrix injury and canalicular disruption were often co-localized and were increased in the lateral (tension) cortex. These changes were partially reversed after adaptation. Loss of canalicular staining and the presence of blind-ends in regions with matrix injury were suggestive of rupture of dendritic cell processes. Taken together, these data support the general hypothesis that the osteocyte syncytium can respond to cyclic loading and influence targeted remodeling during functional adaptation. Changes in the appearance of the osteocyte syncytium were found in fatigue-loaded bone with and without linear microcracks. We hypothesize that the number of dendritic cell processes that experience load-related disruption may determine osteocyte metabolic responses to loading and influence targeted remodeling.
Asunto(s)
Adaptación Fisiológica/fisiología , Fracturas por Estrés/patología , Células Gigantes/patología , Osteocitos/patología , Soporte de Peso/fisiología , Animales , Matriz Extracelular/metabolismo , Curación de Fractura , Células Gigantes/metabolismo , Masculino , Microscopía Confocal , Osteocitos/metabolismo , Ratas , Ratas Sprague-DawleyRESUMEN
Failure of bone adaptation to protect the skeleton from fatigue fracture is common, and site-specific accumulation and coalescence of microcracking in regions of high strain during cyclic loading is considered a key factor that decreases the resistance of whole bones to fracture. We investigated the effect of cyclic fatigue loading on the monotonic structural properties of the rat ulna during accumulation and coalescence of microcracks. Cyclic end-loading of the ulna was performed at 4 Hz ex vivo at an initial peak strain of -6000 muepsilon to 20% loss of stiffness (n = 7) or 40% loss of stiffness (n = 7) bilaterally. A 0% loss of stiffness monotonically loaded control group (n = 7) was also included. Volumetric bone mineral density (vBMD), ultimate strength (F(u)), stiffness (S), and energy-to-failure (U) were determined in one ulna and in the contralateral ulna vBMD, cortical bone area (B.Ar), maximum and minimum second moments of inertia (I(MAX) and I(MIN)), microcrack density (Cr.Dn), microcrack mean length (Cr.Le), and microcrack surface density (Cr.S.Dn) were determined. In two additional groups of rats, cyclic end-loading of the ulna was also performed ex vivo unilaterally to 20% loss of stiffness (n = 10) and 40% loss of stiffness (n = 10) and then vBMD, F(u), S, U, B.Ar, I(MAX), and I(MIN) were determined bilaterally. Fatigue loading had incremental degradative effects on ulna structural properties. This decreased resistance to fracture was associated with accumulation and coalescence of branching arrays of microcracks within the cortex of the ulna. Microcracking was most prominent in the middiaphysis and corresponded to the region of the bone that fractured during monotonic structural testing. Fatigue loading influenced the relationship between bone cross-sectional geometry and vBMD and ulna structural properties. At 40% loss of stiffness, F(u), S, and U were all significantly correlated with cross-sectional bone geometry and vBMD, whereas this was not the case at 20% loss of stiffness and with the 0% loss of stiffness monotonic control ulnae. We also found a biologically significant individual animal effect. Larger ulnae required a higher number of load cycles for fatigue to develop, retained higher strength, and accumulated a greater amount of microcracking at the end of the cyclic fatigue testing. Small increases in bone size and density can substantially improve the resistance of whole bones to fracture as microcracking accumulates and coalesces during cyclic fatigue loading.
Asunto(s)
Fracturas por Estrés/patología , Fracturas por Estrés/fisiopatología , Fracturas del Cúbito/patología , Fracturas del Cúbito/fisiopatología , Animales , Densidad Ósea , Fuerza Compresiva/fisiología , Diáfisis/patología , Diáfisis/fisiopatología , Masculino , Ratas , Ratas Sprague-Dawley , Cúbito/patología , Cúbito/fisiopatología , Soporte de Peso/fisiologíaAsunto(s)
Calcinosis/veterinaria , Enfermedades de los Perros/diagnóstico , Enfermedades de los Perros/terapia , Litotricia/veterinaria , Articulación del Hombro , Tendinopatía/veterinaria , Animales , Calcinosis/complicaciones , Calcinosis/diagnóstico , Calcinosis/terapia , Enfermedades de los Perros/diagnóstico por imagen , Perros , Miembro Anterior , Cojera Animal/etiología , Masculino , Radiografía , Tendinopatía/complicaciones , Tendinopatía/diagnóstico , Tendinopatía/terapiaRESUMEN
The structure and function of an automated nosometric system, created by the authors, for prognosis of the risk of delivery of a child with low weight is described. The system is designed for health services, which give direction to parturient (public health sectors) and obstetric wards without technique and specialists for management of such children. The summarized extract is made on 883 cases, but verification--on 463 cases. The total effectiveness of the system is 82.1% against 66.25% of exact results during intuitive prognosis.